1. Field of the Invention
The present invention relates generally to the production of adhesive resins from biomass materials and, more particularly, to the treatment of fast-pyrolysis oils to make phenol-formaldehyde resins from lignocellulosic materials. Specifically, the present invention relates to a process for making phenol/neutral fractions suitable in the production of phenolformaldehyde resins from fast-pyrolysis oils derived from lignocellulosic materials.
2. Description of the Prior Art
Adhesive resins are utilized in a wide variety of applications including the bonding of wood layers to manufacture plywood (resoles), the formation of molded pieces and articles (novolaks), and the like. There are certain disadvantages, however, to existing techniques for the manufacture of phenolic resins. Phenol has been traditionally derived from petroleum-based products. Because the production of petroleum-based phenol can be quite expensive, there have been efforts in recent years to at least partially substitute the phenol in such resins with inexpensive phenols derived from wood-based products or extracts. More specifically, phenols derived from bark, wood chips and the like has been looked at as a potential substitute for petroleum-based phenol in such resins.
The pyrolysis of biomass, and in particular lignocellulosic materials, is known to produce a complex mixture of phenolic compounds which are derived primarily from the lignin fraction of the biomass. In nature, lignin acts as an adhesive to bind the cellulose fibers together. Therefore, lignin and lignin-derived material from wood seem like a natural starting point for the development of biomass-based adhesive resins. Sources for such phenolic materials include black liquor from kraft pulping and other pulping processes, where the lignin is present in a stream which is commonly burned to recover process heat and chemicals. Unfortunately, these lignins are generally not very reactive after recovery for a variety of reasons, such as high molecular weight, chemical modification during recovery due to condensation reactions and the like, and lack of reproducibility of proprieties. Various types of pyrolysis processes have also been utilized, frequently yielding similar kinds of results. Fast-pyrolysis, however, has proven to be an exception to this.
Fast-pyrolysis of biomass features the depolymerization of cellulosic, lignin, and hemicellulosic polymers which produces an oil having a relatively low molecular weight and which has considerable chemical activity under proper conditions. Crude pyrolysis oil apparently undergoes a limited amount of repolymerization upon physical condensation. However, the thermal stability of fast-pyrolysis oils at room temperature is qualitatively quite good implying a good shelf life for the oils, although at 100.degree. C. the crude oils solidify overnight. Solidified pyrolysis oils are characterized by their low strength and brittleness. The potential of pyrolysis products for use in adhesive resins is not a new concept, as indicated above, but the efficient and cost-effective reduction of this to practice has been an elusive goal over many years.
The general approach of producing phenols from biomass has previously been to purify the phenolic fractions present in the pyrolysis oils by the use of solvents to partition the constituents by differences in solubility and reactivity. Different variations of solvents, reagents, and sequence of extractions have been developed in the past, and this has resulted in different partitioning coefficients for a couple of hundreds of chemical compounds known to be in pyrolysis oils, and therefore produced extracts having differing relative compositions. Another significant difference between various research efforts pertaining to this area in the past has been the type of pyrolysis used to produce the oils used as feed in the extraction process. These include updraft gasification, entrained fast-pyrolysis, and fluidized bed fast-pyrolysis, all at atmospheric pressures, as well as slow, high pressure liquefaction processes. In addition, both hardwoods and softwoods have been used as feedstock in the past for the oil forming processes. These differences in extraction and pyrolysis processes, coupled with the differences in feedstock, yield different materials as products. Thus, as indicated below, the usefulness of a particular extract as an adhesive component is quite different, one from the other.
U.S. Pat. No. 4,209,647 and No. 4,223,465 disclose methods for recovering phenolic fractions from oil obtained by pyrolysis of lignocellulosic materials and the subsequent use of that fraction in making of phenol-formaldehyde resins. However, these processes use pyrolysis oils which are usually formed at ill-defined temperatures and which have undergone phase separation cracking and some condensation, and suffer from very low yields.
A number of other patents including U.S. Pat. No. 2,172,415, No. 2,203,217, No. 3,069,354, No. 3,309,356 and No. 4,508,886 as well as Japanese Patent No. 38-16895 all disclose a variety of processes for recovering phenolic fractions from oils derived from biomass materials and oil resources. These processes vary in the particular procedures and techniques utilized to ultimately separate the phenolic fractions as well as the procedures utilized to derive the oil from the biomass or other feed material. However, they all have a common thread linking them in that the ultimate end product is a phenolic fraction, which is desired to be as pure as possible. This phenolic fraction is then utilized to produce phenol-formaldehyde resins. The phenol substitutes usually were slower than phenol derived from petroleum-based products. The complex procedures disclosed in there references to produce relatively pure phenolic fractions are not particularly economical. Thus, there is still a need for a process designed to produce pyrolysis oils from lignocellulosic materials and then extract a phenolic composition from such oils which is capable of functioning as efficiently as petroleum-based phenols in the formation of phenol-formaldehyde resins and which is less expensive to produce.